THEORY OF OPERATION
3-3. Detectors
(1)Paper-Out Detector
The paper-out detector is located at the paper entry slit. The detector consists of a reflective photosensor. The photosensor’s phototransistor remains ON while paper is present. It goes OFF when paper runs out, generating output of a paper-out signal.
(2)Black-Mark Detector
This detector senses black marks indicating print start positions. The detector is useful only with specially marked paper. Like the paper-out detector, the black-mark detector consists of a reflective photosensor. The photosensor’s phototransistor goes OFF when a black mark appears.
R
GND
+5V
Detection signal 
R
R
Paper GND
+5V
Detection signal 
R
(Reflective photosensor)
(Reflective photosensor)
Fig. 2-15 Paper-Out Detector | Fig. 2-16 Black-Mark Detector |
(3)Label Detector
The transmissive detector is used to detect print-start positions for labels. It operates by detecting the difference in light transmission between backing-only and backing-plus-label portions of the paper.
LightLight
Label paper
| Quantity of | Backing paper |
| Quantity of |
| transmitted light |
| transmitted light |
| |
Fig. 2-17
5V
Paper
Detection signal 
GND
Fig. 2-18 Label Detector
